Here are beautiful maps of Belgium in 1777. The site is in french, but you only have to select a box on the map, and then on the blue link in "résultats" in the above part of the page.
It is not possible to download the map themselves, but only to view them (unless you want to pay 40 euros for a single map...).

http://www.ngi.be/FR/FR1-4-2-3.shtm